The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Aspects of the present invention relate to a wind turbine comprising a cooling circuit, particularly for discharging heat generated by electrical equipment in the wind turbine.
Energy conversion results in energy being lost in the form of heat. In the main driving line of a wind turbine, which is typically mounted in the nacelle, losses occur in the gears, at the bearings, and in the generator or at other control units, such as, e.g., in the hydraulic systems or similar control and regulation pitch and yaw units. For gearless direct drive wind turbines the main losses occur at the generator area in the nacelle. For the power supply, losses occur at the power transformer and in possibly present other power electronics, e.g., in the rectifier.
Generators in wind turbines are typically cooled by an air flow through the air gap between the generator rotor and stator, and over the sections containing the coils where most of the heat is generated. Corrosion sensitivity requires that the materials near the air gap should only be subjected to dry and clean air. For this purpose, closed air cooling circuits are generally used. Closed cooling circuits have the advantage that no outside air needs to enter the generator area which is particularly useful for offshore wind turbines where the outside air is humid and has a high salt particle content. A secondary air-to-air system can be used to transfer the heat to the outside air. Alternatively, air from the turbine interior can be circulated via the air gap. For turbines comprising a steel tower, the tower wall can be used to dissipate the heat from the air circulation system. In a closed or partly closed cooling circuit, the cooling air circulates within the wind turbine from its nacelle to the tower or to the base of the wind turbine and the energy stored by the coolant, such as air, during the cooling is dissipated via the tower wall of the wind turbine. The tower of the wind turbine is exposed to wind, enhancing the effectiveness of the wind turbine tower as a cooling element or a heat exchanger. In order to use the complete tower length effectively the air should be forced to have a vertical flow, top-down or bottom-up.
WO 01/06121 discloses a wind turbine with a closed cooling circuit and a tower being integrated into the cooling circuit as a cooling element. Channels guide the hot air closely along the interior side of the tower wall. Similarly, in DE 100 16 913 A spiralling channels are used to guide hot air along the inner surface of a wind turbine tower wall. This way, a closed cooling circuit can be obtained circulating hot air which is cooled by the tower wall.
The channels used in WO 01/06121 and DE 100 16 913 A complicate the construction of the wind turbine tower. Moreover, the passage of the channel forms a bottle neck for the circulating amount of air, which may not be sufficient for effective cooling of the generator area.